Handwriting is traditionally performed on a writing surface, such as paper, with an ink-dispensing pen or other writing instrument, such as a pencil, or paint brush that leaves a visible marking on the writing surface. The markings are expected to be understandable by human readers.
Recently, electronic handwriting has been done on planar X-Y digitizing pads using a stylus employed to simulate handwriting upon the pad to create an electronic facsimile of handwriting. The digitizing system collects an array of X-Y coordinates of pixels corresponding to the curve tracing positional points of a stylus tip on the pad. Usually the X-Y arrays are gathered and stored as positional arrays, and made discernible to a human reader when rendered upon an X-Y display, but the renderings are rarely discernible as readable text by an electronic device.
Attempts to make handwriting discernible as machine-readable text have concentrated on handwriting recognition of the X-Y traces by translation into binary coded text after affine transformation of the X-Y trace. Other techniques of recognition of the X-Y traces employ stochastic recognition based on various randomness assumptions using a statistical model. Other attempts with more deterministic techniques of recognition of the X-Y traces use velocity profiling in on-line recognition and forward search in batch recognition. Many similar X-Y trace recognition efforts have resulted in numerically intense algorithms which tend to restrict the recognition process to off-line batch processing, conducted as a separate procedure long after the writing has been done and the X-Y trace stored.
More recently, on-line recognition systems have dispensed with natural hand-writing and created specialized pen-stroke shorthand for letters of the Latin alphabet, Arabic numerals, and punctuation marks, such as an electronic stylus recognition system. Field experience has shown that recognition error rates are high enough to cause manufacturers to begin supplanting these systems with keypads and software keyboards. Miniaturized keypads are slow when compared to normal handwriting speed. Full-sized keyboards, although faster in use than miniature keyboards, are too cumbersome for many purposes.
Devices that track X-Y motion in true geometry exist in the form of analog joysticks. These may be used as actuators for simulations and as gaming input devices, where a band-held game controller may incorporate an analog joystick that permits tracking of directional inputs about 360 degrees around an action reference point, and is small enough to be manipulated by a finger tip. The cited range of 360 degrees signifies that the joystick spans a projection of the X-Y plane, but does not span a radial distance, i.e., the joystick is not operable to span a projection along the Z-axis. This is because the range of each joystick sensor is less than the radial range needed to be spanned.
The cited joystick may utilize optical quadrature sensor wheels over two orthogonal axes of rotation. Such a configuration may suffice for directional control over a planar range, but is inadequate for the capture of natural handwriting strokes because the capture of natural handwriting strokes requires a depth sensor. A depth sensor may be adapted to enable the device to distinguish handwriting strokes or hand movements that create writings or markings and those hand movements that are not intended to and do not create writings or markings.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art through comparison of such systems with embodiments presented in the remainder of the present application with reference to the drawings.